An integrated circuit is typically fabricated on a single chip of silicon or other semiconductor material, also referred to as a die, which is then packaged for use. During packaging, the integrated circuit die is wire-bonded to leads of a leadframe. A robotic bonding tool may be used in this operation. Such a tool generally includes a surface/wire-feed detection system that detects bond pads of the integrated circuit die, determines the height coordinates of the bond pads, and wire-bonds the bond pads to the leadframe. After detecting the location of bond pads on the surface of the die, the bonding tool is lowered to a starting bond pad to determine the height coordinate of the pad and to adjust ultrasonic power without bonding. This first “learning touch” is performed without knowledge as to the accuracy of the height coordinate. As a result the bonding tool frequently overestimates the height coordinate and the tip of the bonding tool, also referred to as a capillary/wedge, forcefully contacts the starting bond pad. This forceful contact may cause significant damage to the bond pad, the underlying dielectric films, and the die, resulting in bonding difficulties in the integrated circuit.
Further, since the die is rarely staged precisely flat for a bonding operation, the bonding tool may determine the tilt of the integrated circuit die. This is traditionally accomplished by determining the height coordinates of selected bond pads at opposing locations on the die. The measured height coordinates of these bond pads are then used by the robotic bonding tool to interpolate the height of the remaining bond pads, such that bonding may be performed at the correct height coordinate for each bond pad. However, the selected pads may be damaged in the same manner as the starting bond pad as described above.
Several attempts have been made to solve the problem of the potentially damaging “learning touch” of the bonding tool. First, it has been proposed to more precisely measure setup procedures, so that the “learning touch” is manually executed for each individual die. However, this may result in decreased manufacturing speeds, as well as additional difficulties in the case of a die which includes mechanically-weak low-k dielectric films under its bond pads. It has also been proposed to retrofit bonding tools with atomic force microscopy hardware, however, such hardware add-ons are very expensive. The problem may also be ignored, relying on the likelihood that any failures will be caught during burn-in testing. However, there is not always an early electrically-detectable signal indicating that damage has been done during bonding. Instead, the realization may come when the device has been operating in the field for months or years, undesirably affecting device reliability.
Thus, a need exists for a method and apparatus for determining bond pad height coordinates in an integrated circuit without causing damage to the pads, dielectric films, or die, and without the other drawbacks of the conventional techniques.